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EARTHQUAKES. 



South x\merica of the earth having quaked in- 

 cessantly for several days together ; but I only 

 know of shocks that were felt almost every 

 hour for several months, having occurred far 

 from any volcano^ on the eastern slopes of the 

 Alps of Mont-Genis, about Fenestrella and Pig- 

 nerolo, from April, 1808 ; in the United States 

 of America, betwixt New Madrid and Little 

 Prairie(i"), to the north of Cincinnati, after 

 December, 1811 ; in the Paschalic of Aleppo, 

 in the months of August and September, 1822. 

 As the vulgar mind can never rise to general 

 views, and therefore always ascribes great phe- 

 nomena to local processes of the earth or of 

 the air, wherever succussions continue for any 

 length of time, fears for the appearance of new 

 volcanoes take their rise. In single,* rare in- 

 stances, this fear has indeed shown itself well- 

 founded, as in the case of the sudden rise of 

 volcanic islands, and in the production of the 

 volcano of JoruUo, a new mountain, rising 1580 

 feet above the old neighbouring level, on the 

 29th of September, 1759, after ninety days of 

 earthquakes and subterraneous Ihunderings. 



Could we have daily news of the state of the 

 whole of the earth's surface, we should, in all 

 probability, become convinced that some point 

 or another of this surface is ceaselessly sha- 

 ken ; that there is uninterrupted reaction of the 

 interior upon the exterior going on. This con- 

 stancy and general diffufiion of a phenomenon, 

 which is probably connected with the high tem- 

 perature of the deepest strata of the earth, ex- 

 plains its independence of the nature of the 

 rocky masses among which it is manifested. 

 Shocks of an earthquake have been experien- 

 ced even in the loosest alluvial deposits of Hol- 

 land, around Middleburg and Flushing. Gran- 

 ite and mica slate are shaken in the same way 

 as mountain limestone and sandstone, as tra- 

 chytic and amygdaloidal formations. It is not 

 the chemical nature of the constituents, but the 

 mechanical structure of the mineral species, 

 that modifies the propagation of the motion (the 

 Wave of sucGussion). Where the wave pro- 

 ceeds regularly along a coast, or by thg foot, 

 and in the direction of a mountain-chain, it is 

 occasionally observed that there is an interrup- 

 tion suffered at certain points. This has been 

 noticed for centuries. The undulation advan- 

 ces along the depths, but at the points in ques- 

 tion it is never felt at the surface. The Peru- 

 vians say of these unshaken superior strata, 

 that " they form a bridge"(^*'). As mountain- 

 chains appear upheaved through fissures, the 

 walls of these cavities may very well favour or 

 influence the course of the undulations that run 

 parallel with the chain ; occasionally, however, 

 the waves of succussion cut across several 

 chains, almost at right angles. We thus see 

 them break through the littoral chains of Vene- 

 zuela and the Sierra Parime in South America. 

 In Asia, the earthquakes of Lahore and the foot 

 of the Himalayas (Jan. 22d, 1832) were prop- 

 agated transversely through the chain of Hin-' 

 doo-Cusch to Badakhchan, to the Upper Oxus, 

 and even to Bokhara(^*°). Unfortunately, too, 

 the circles of concussion enlarge, in conse- 

 quence of a single extremefy Violent shock. It 

 is only since the destruction of Cumana (14th 

 Dec. 1797) that every shock of the southern 

 coast is felt in the mica-slate strata of the pen- 



insula of Maniguarez, which lies opposite the 

 limestone or chalk-hills of the fortress. In the 

 almost incessant undulations of the ground of 

 the valleys of the Mississippi, Arkansas, and 

 Ohio, which occurred from 1811 to 1813, the 

 progress of the motion from south to north 

 was very striking. It was as if subterranean 

 impediments had been gradually overcome, and 

 the wave of commotion then advanced upon 

 each occasion along the way which had been 

 opened up. 



If an earthquake appear, at first sight, to be 

 a phenomenon of motion wholly dynamical, 

 having reference to space only, it is still recog- 

 nized, on the grounds of the most careful ex- 

 perience, that it is not only competent to raise 

 whole districts above their old level (Ulla-Bund, 

 eastward from the delta of the Indus, for ex- 

 ample, after the earthquake of Cutch, in June, 

 1809, and the coast of Chili, in November, 

 1822), but farther, that during the shock, hot 

 water (Catania, 1818), hot steam (valley of the 

 Mississippi, near New Madrid, 1812), mephitic 

 or irrespirable gases, which are injurious to the 

 pasturing herds and flocks of the Andes, mud, 

 black smoke, and even flames (Messina, 1782, 

 Cumana, 14th Nov. 1797), have been dischar- 

 ged. During the great earthquake of Lisbon, 

 Nov. 1, 1755, flames and a column of smoke 

 were seen to rise from a newly-formed fissure 

 in the rock of Alvidras, near the city. The 

 smoke became on each occasion where it ap- 

 peared, by so much the more dense as the sub- 

 terraneous noise increased in loudness(^®^). 

 When the town of Riobamba was destroyed in 

 1797, the earthquake was not accompanied by 

 any eruption of the volcano which is so close 

 at hand ; but Moya, a singular mass, compound- 

 ed of carbon, crystals of augite, and the silice- 

 ous coats of infusory animalcules, was pushed 

 out of the ground in numerous small and pro- 

 gressive cones. The escape of carbonic acid 

 gas during the earthquake of New Granada 

 (16th Nov. 1827), from fissures in the Magda- 

 lena valley, caused the suffocation of many 

 snakes, rats,' and other creatures that live in 

 holes. Sudden changes in the weather, too, 

 the setting in of the rainy season at unusual 

 periods in the tropics, have occasionally fol- 

 lowed great earthquakes in Quito and Peru. 

 Do gaseous fluids, escaping from the interior 

 of the earth, then become mingled with the at- 

 mosphere 1 or, are these meteorological pro- 

 cesses the effect of a disturbance of the atmo- 

 spherical electricity by the earthquake'? In 

 the countries of tropical America, where some- 

 times not a drop of rain falls for ten months, 

 the inhabitants look upon repeated shocks of 

 earthquakes, which cause no danger to their 

 low cane huts, as a happy indication of plenty 

 of rain, and consequently of fertility. 



The intimate connection of all the phenom- 

 ena now described is still buried in obscurity. 

 Elastic fluids are undoubtedly the cause, as 

 well of the slight and uninjurious tremblings of 

 the earth, which continue for many days (as in 

 1816 at Scaccia, in Sicily, previous to the ele- 

 vation of the new island called Julia), as of the 

 frightful explosions which are announced by 

 noises. The focus of the mischief, the seat of 

 the moving power, lies deep beneath the crust 

 of the earth ; how deep, we know even as little 



